Ordinary Meeting, 2008 May 28
The May Sky
Mr Hurst remarked that May and June were never good months for observers on account of their having such short hours of darkness, and so he opened with an update on NASA's Phoenix and Mars Reconnaissance Orbiter (MRO) missions to Mars. Phoenix had landed successfully on Mars' north polar plane three days earlier, on 2008 May 25 at around 23:45 UT. A few images of the landing site had already appeared on the NASA website, but analysis of them was clearly at an early stage. The speaker explained that the orbit of MRO had been adjusted in the past few days to place it close to Phoenix's landing site at the time of its descent. Consequently, it had been able to use its HiRISE camera to obtain a series of high-resolution images of Phoenix's entry into the Martian atmosphere. NASA's press releases were advertising these images as the first ever taken by one spacecraft of another's landing. More importantly, images of the deployment of Phoenix's parachutes would provide valuable feedback for the design of future missions.
Continuing on the theme of MRO's recent observations, Mr Hurst added that it had flown close by Phobos, the larger of Mars' two moons, on 2008 March 23, and had used its HiRISE camera to obtain a pair of images at distances of 6,800 and 5,800 km from the moon's surface. He explained that both Phobos and its smaller neighbour Deimos were widely thought, based upon their small sizes and unusual compositions, to be asteroids which had been captured by Mars' gravitational field from the neighbouring asteroid belt which lay between Mars and Jupiter. MRO's images showed the large Stickney impact crater on Phobos' surface, together with a striking series of grooves which covered almost half of the moon's surface and appeared to radiate outwards from a point close to, but not quite aligned with, the centre of Stickney.
Turning to discuss prospects for observing the planets, the speaker mentioned that over the past few days Mars had been in conjunction with the Beehive Cluster (M44); it had made its closest approach on the evening of May 22–23 at a distance of around 15' from the centre of the cluster, skimming among its outer members. This had been a challenge to observe, given the difference in brightness between Mars and M44, and although the speaker had seen some amateur images from abroad, noone in the audience had observed it. A much easier conjunction to observe had been the occultation of half of the Pleiades (M45) by the Moon on May 6. Mercury had also been nearby at the time, lying a mere 6° away. The speaker noted that this conjunction had been very widely photographed, and many novice astrophotographers had even managed to get images without using tripods.
Moving out to the gas giants, the speaker reported that Jupiter was now rising at 11pm UT, having emerged from its solar conjunction of late 2007 December, and would reach opposition on 2008 July 9. John Rogers, Director of the Jupiter Section, was reporting that early observations from the new apparition were showing that the large-scale turbulence and storms which had plagued the planet for the past two years were continuing. A small new red anticyclonic oval in the South Tropical Zone, dubbed the Baby Red Spot, was heading for a conjunction with the Great Red Spot in late June or early July. It was uncertain whether the two spots would pass one another or merge. At around the same time, another prominent red anticyclonic oval, Oval BA, itself dubbed the Little Red Spot, would be at a similar longitude but lying a few degrees to the south.
Saturn was also visible in the evening sky at present, setting at 1am UT; it had passed opposition on February 24. Amateur planetary imagers were currently interested in two prominent white spots visible in the planet's South Tropical Zone, which could be seen visually and photographically through telescopes of 20-cm aperture and larger.
Mr Hurst then moved on to congratulate Mr Peter Birtwhistle upon the discovery of his 100th asteroid, 2008 GE3, on April 7. The speaker noted that this object's magnitude had been a mere 20.7 at discovery; the rise of efficient robotised minor planet surveys had meant that amateurs needed to be able to catch asteroids at such faint magnitudes in order to beat the competition. The discovery of 100 objects was surely a testament to Mr Birtwhistle's dedication to the task. The speaker noted that Mr Birtwhistle's tally of asteroid discoveries might soon overtake the tallies of amateur supernova hunters. He noted, however, that new asteroid discoveries needed follow-up observations over longer timescales than new supernovae. Before an asteroid could be confirmed and numbered as a new minor planet, a secure orbit needed to be determined for it, based upon observations from several oppositions. Of Mr Birtwhistle's 100 discoveries, to date only 9 had become numbered minor planets. Of the rest, 50 had been observed at multiple oppositions and were expected to receive numbers soon, while the remaining 41 had only been observed at one opposition.
The speaker closed with a review of the comets in the sky at present. None were especially bright, although he drew attention to comet 2007 W1 (Boattini), which had recently outburst to mag 6.3, around two magnitudes brighter than had been expected. Lying in Puppis, it was not visible from the UK at present, but it would be more favourably situated in July and August. On August 1 it would pass close by π Ari, and then, after sweeping north through Aries in August, it would pass Hamal at the end of the month. If it remained in outburst, it could be expected to be around mag 8/9 during this period, and so within range of binoculars.
Following the applause, the President adjourned the meeting until Saturday June 28.
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Dominic Ford